Most OSR community is based around Dungeons and Dragons, however like a lot of Europeans my first encounter with roleplaying or fantasy gaming was not through D&D itself by through reflections of those who had read a copy or heard of the idea and created their own.
Like a lot of early British roleplayers my nostalgia is really for Fighting Fantasy, a formative experience that was notable different in tone from American fantasy while being composed of much the same tropes.
Troika! is an attempt to create a retro-clone that brings together Warhammer and Fighting Fantasy into a simple rules system that bakes weird fantasy into core of character creation in the same way that the Ratcatcher career did in the 1980s.
The basic mechanics are pretty simple. Mainly 2d6 are used and the basic characteristics are Skill, Stamina and Luck.
If you are attempting something against the environment you try to roll under your Skill on two dice, if contested you roll and add, aiming for the highest total.
Combat is pretty interesting, with the use of an initiative bag filled with counters to determine who has the next action and rounds being variable length due to a turn end token.
One of my bugbears with OSR games is also fixed with the use of a damage table that ensures that damage is very consistent and occasionally poor and sometimes high.
My biggest issue with the game (apart from some of the inconsistently sloppy game design) is that I find a lot of the esoteric fantasy over the line into incoherence and obscurity.
Instead of being a stepping stone to your own interpretation some of the ideas that are enshrined in the rulebook are mood-killing whimsical (brawlers are from the Society of Beef Steaks, one of the backgrounds is as a Befouler of Ponds), story killing (spell results that turn the caster into a pig) or just impenetrable (the Cacogen).
There's a lot to admire in Troika!, in particular the way that a particular view of weird fantasy is invoked through the origin stories, items and abilities of the characters. I think it might be one of those games that I might have to play to really understand.